Fluid power is the transmission of forces and motions using a confined and pressurized fluid to convert the forces/motions to a more useable form and distribute them. In hydraulics, the fluid is a liquid (usually oil), whereas pneumatics uses a gas (usually compressed air). Comparing with mechanical and electrical power, fluid power systems easily produce a linear motion using hydraulic or pneumatic cylinders, whereas electrical and mechanical methods usually must use a mechanical device to convert a rotational motion to a linear motion.
Fluid power systems can generally transmit equivalent power within a much smaller space than mechanical or electrical drives can, especially when extremely high force or torque is required. Fluid power systems also offer simple and effective control of direction, speed, force, and torque using simple control valves. For example, hydraulic systems can be finely controlled for precision motion applications because the oil has high modulus.
Furthermore, the fluid power system is also famous for its compactness and flexibility. Fluid power cylinders are relatively small and light for their weight and flexible hoses allows power to be snaked around corners, over joints and through tubes leading to compact packaging without sacrificing high force and high power. Due to the advantages stated above, the fluid system has been widely used and developed in the field of medical devices, including the body supporting equipment that can not only support the body weight, but also generate responsive changes according to the body posture.
U.S. Pat. No. 6,009,580 to Caminade et al. discloses a method and apparatus for supporting a body element. The apparatus includes at least one support device with at least one closed or controlled-release chamber, a filling device and an emptying means device for filling said chamber with a filling fluid and emptying the fluid from the chamber, and a distance-measurement device for measuring the distance between a top face and a bottom face of the chamber. More specifically, Caminade measures the penetration corresponding to a predetermined float line to determine when to fill or empty the chamber, as shown in FIG. 1. However, the float line for each person would be different and the penetration is actually difficult to measure. Thus, if the timing to fill or empty the chamber is inappropriate, the person being supported may feel uncomfortable.
U.S. Pat. No. 6,763,541 to Mahoney et al. discloses an air bed having a pump and a relief valve operably connected with a control box. The control box is capable of being programmed or receiving scripted information from a media file such that timed pressure changes may be made in the air bed by operation of the pump and the relief valve. These changes are synchronized with a message being played by a media player. Thus, the air bed interacts with a person lying on the bed. However, Mahoney seems to emphasize on how the user can interact with the air bed, but does not particularly teach how to precisely control the timing to fill or empty the bladder(s) that is used to support the person.
U.S. Pat. No. 8,090,478 to Skinner et al. discloses an apparatus for supporting a patient that includes a patient support surface, at least one fluid containing bladder and a pressure control assembly. The at least one bladder is positioned to provide support for the patient when the patient is bearing on the patient support surface for at least a portion of the patient support surface. The pressure control assembly is operably coupled with the at least one bladder and regulates the fluid pressure within the at least one bladder. The pressure control assembly includes a programmable controller which is programmed to monitor sensed pressure values of the fluid pressure within the at least one bladder and adjust the fluid pressure within the at least one bladder. The controller is programmed wherein an acceptable range of pressure values is defined and the controller initiates adjustment of the fluid pressure within the at least one bladder when a sensed value is located outside the acceptable range of pressure and a time period following the sensing of the sensed value has elapsed without the fluid pressure within the at least one bladder returning to the acceptable range of pressure, where the time period has a variable length. However, the supporting apparatus includes a limited number of bladders that is used to provide the support of the patient, and the control of the bladder is merely through the pressure control assembly. Like Caminade and Mahoney, Skinner does not suggest how to precisely control the pressure of the bladders in the supporting apparatus.
Therefore, there remains a need for a new and improved system to precisely control a three-dimensional surface to overcome the problems stated above.